A camshaft for an internal combustion engine generally comprises a shaft having integrally formed bearing journals and cam lobes, and a drive gear. The drive gear may be integral with the camshaft or may be machined separately and secured to an end of the camshaft. Most frequently, the camshaft is a forging or a casting. The journals and cam lobes are machined and/or ground to desired configurations. Manufacturing a forged camshaft is expensive. Once the forging is produced, only limited adjustments may be made in the rotational location and profiles of the cam lobes in the final machining and grinding processes. Considerable expense is involved in modifying the forging dies to obtain a different cam lobe position and profile in the forging.
According to another prior art method for manufacturing camshafts, the shaft, the cam lobes, the journals and the drive gear are manufactured as separate components. The lobes, journals and gear were secured to the shaft either by an interference fit, by deforming the shaft, or by welding. When welded, the welding heat adversely affected the temper of the attached parts. This required hardening subsequent to welding. According to a method described in U.S. Pat. No. 3,999,277, the lobes, journals and drive gear could be designed for an interference fit on the shaft and placed in a holder wherein they were aligned for receiving the shaft and held in their final position relative to each other. The lobes, journals and drive gear in the holder were then heated and a cooled shaft was inserted through aligned holes in the parts. When the assembly cooled, the lobes, journals and gear became secured on the shaft by an interference fit. Finally, each part was further secured to the shaft with a fillet weld. However, fillet welding can transfer sufficient heat to the cam lobes, for example, to adversely affect their temper. This requires subsequent heat treating to restore the surface hardness of the cam lobes.